Reviews registered with third-party review collectors such as Reviews.co.uk tend to be the most reliable as they are reviewed by verified customers and are harder to manipulate by an unscrupulous dealer. Be more wary of online marketplace reviews that can sometimes be faked.
A small handful of bad reviews may not be a red-flag. It is after all, impossible to please everyone, all of the time. But do use your judgement. Poor quality products and bad customer service is often a pattern that you can spot – don’t think the experience will be different, just because it’s you!